Electrochemical elements, including batteries, are constructed from an electrolyte where ion migration occurs and an electrode where electrons are donated to migrated ions. In a case in which the electrolyte is a liquid where a support salt is dissolved in a solvent, it is difficult to make the electrochemical element smaller or thinner since a container for housing the liquid is necessary. The electrochemical elements, particularly lithium batteries, have been vigorously investigated in order to achieve a battery with a higher energy density on the basis that lithium is a substance with a small atomic weight and a large ionization energy, and nowadays have been widely used for electric current sources of portable instruments. On the other hand, internal energy thereof has increased due to increase of content of active materials, and also content of flammable organic solvents in electrolyte liquids has increased; therefore, in recent years, the lithium batteries have been closed up in terms of safety thereof along with being universally applied. Nowadays, development of all-solid-state batteries has been carried out in which a solid electrolyte material of nonflammable substance is used from the viewpoints of small-sizing, thin-sizing, and safety thereof.
An electrode used for the all-solid-state batteries is produced through steps of coating and drying a slurry for battery electrodes that contains an electrode active material and a binder composition for batteries dissolving a polymer in an organic liquid medium on a surface of a current collector, and laminating an electrode layer on the current collector by press-working the resulting coating, for example.
In the all-solid-state batteries, not only adhesion to the current collector but also high adhesion to a solid electrolyte layer disposed between a pair of electrodes is required to the electrode layer formed from the slurry for battery electrodes. In addition, in order to improve electrical conductivity of the solid electrolyte layer, suppression of an amount of binder used in relation to the solid electrolyte material in the solid electrolyte layer is also required, and thus improvement of the adhesion is further required. For the purpose of improving the adhesion, employment of a polymer with a relatively high polarity as the binder has been investigated (see Patent Documents 1 to 8). In order to dissolve such a polymer, a highly-polar organic liquid medium such as N-methylpyrrolidone must be used.
However, such a highly-polar organic liquid medium deteriorates or degrades an electrode active material, as a result, there arises a problem in that electric performance of electrodes or batteries using them are impaired. On the other hand, in cases of using a nonpolar organic liquid medium dispersing a polymer with less influence on the electrode active material, it is difficult to form a uniform electrode layer when coating the slurry for battery electrodes on a surface of the current collector by a process such as a doctor blade process and a spin coating process in particular, and thus workability is poor when producing electrodes.
For the countermeasure, in order to avoid the problems described above, a low-polar polymer soluble in a nonpolar or low-polar organic liquid medium has been investigated for the purpose of employing as a polymer for forming a binder so as to variously improve a structure etc. of the polymer and to enhance the adhesion etc. (see Patent Documents 8 to 11); however, improvement of the adhesion is not so remarkable in the technology until now.